1. Field of the Invention
The present invention relates, in general, to refrigerators. More particularly, the invention relates to a cold-accumulation type refrigerator using cold-accumulation material to cool the interior of a refrigeration compartment.
2. Description of the Prior Art
It is known to provide a refrigerator with a cold-accumulation material in order to enhance the cooling capacity of a refrigerating cycle. An example of such a cold-accumulation type refrigerator is disclosed in Japanese Utility Model Publication No. 53-10586, filed on Oct. 9, 1973 in the name of Kenichi KAGAWA. According to Japanese Utility Model Publication No. 53-10586, an auxiliary evaporator and an auxiliary condenser are placed within a case containing the cold-accumulation material. The auxiliary evaporator and auxiliary condenser are connected in parallel fluid circuit relation with each other in order to increase the operating efficiency of the refrigerating cycle, especially the operating efficiency of a compressor.
Recently, there has been consideration of the use in refrigerators of cold-accumulation materials to even out the power demand during a 24-hour day by utilizing power which is not effectively used, such as night-time power. One such refrigerator is constituted as follows.
A main evaporator is provided for cooling refrigerator compartments and a cold-accumulation evaporator is provided for cooling the cold-accumulation material. A time-controlled changeover device selectively changes the operating mode of the refrigerator. In a first mode of operation (ordinary cooling mode), refrigerant is supplied to a main evaporator to cool the refrigerator compartments. In a second mode of operation, the refrigerator compartments are cooled by the cold accumulation material. In a third mode of operation, the cold accumulation material is cooled by the cold-accumulation evaporator. The cold-accumulation material is installed in a manner permitting it to be cooled by the cold-accumulation evaporator. A thermosiphon is provided in a manner permitting transfer of heat between the main evaporator and the cold-accumulation material. The thermosiphon is constituted by a closed-loop pipeline enclosing an operating liquid therein, such as a refrigerant. In the middle of the night when there is little demand for power, the cold-accumulation material is thoroughly cooled by the cold-accumulation evaporator. For a predetermined time period during the day, when there is greater power demand, refrigerator compartments are cooled by second mode operation, i.e. refrigeration is by means of the cold-accumulation material instead of by first mode operation, i.e. ordinary cooling operation, which requires a large amount of power. During second mode cooling the thermosiphon exchanges heat between the cold-accumulation material and the main evaporator. A compressor, which supplies refrigerant to the main evaporator during first mode cooling and consumes most of power required by the refrigerator, is not operated. Therefore second mode cooling requires less power to cool the refrigerator compartments than first mode cooling.
However, with this type of refrigerator, if a refrigerator compartment door is opened and closed when the room temperature is high, as, for example, in summer, the temperature in that compartment rises due to high-temperature room air flowing into the compartment. This causes the cold-accumulation material cooling operation to be required frequently during the day time period assigned for second mode cooling.
In contrast, when the room temperature is colder, such as, for example, in winter, the amount of temperature rise in each compartment is small even when the refrigerator compartment doors are frequently opened and closed. As a result, the cold-accumulation material cooling operation is only carried out a small number of times during the day time period assigned for second mode cooling. Thus, the frequency of execution of second mode cooling varies because of the effects of room temperature. If the refrigerator is arranged so that the compartments are cooled by second mode cooling operation only for a predetermined time period of fixed length, the cold-accumulation material may still have remaining cooling capacity even when the end of the predetermined time period is reached (such as in winter). Despite the remaining excess cooling capacity, the cooling of the cold-accumulation material (third mode operation) is carried out for its predetermined length of time (at night) even though it probably does not require the same amount of cooling that it would require if all of its cooling capacity had been exhausted, such as in summer. This is wasteful.
On the other hand, if an excessively long time period is set for second mode cooling, the cooling capacity of the cold-accumulation material may be used up before the end of the time period assigned for second mode cooling is finished. This would run counter to the object making the power demand even over the course of a 24-hour day.
Thus far, the arrangements of cold-accumulation type refrigerators have not taken into account the effects of room temperature. Therefore, they have not made fullest use of the cooling capacity of the cold-accumulation material.